Zein, a plant protein that can be isolated from corn or maize, belongs to a family of prolamines that are composed of high amounts of non-polar amino acids, such as proline, glutamine and asparagine. Zein is odorless, non-toxic, biodegradable and water-insoluble, and is therefore an attractive component for many applications.
Zein has been investigated or used as a polymer in the pharmaceutical, medical, food, cosmetic, adhesive and packaging industries. In the food and pharmaceutical industries, zein has been used, for example, to film-coat materials and to form particulate systems such as microparticles or nanoparticles (U.S. Pat. No. 5,679,377 (Bernstein et al.), herein incorporated by reference in its entirety; Liu et al., Biomaterials 26 (2005) 109-115; Lopez and Murdan, J Microencapsulation 23 (2006) 303-314; Zhong et al., Food Biophysics 3 (2008) 186-190; Parris et al., J Agric Food Chemistry 53 (2005) 4788-4792).
Various methods of forming zein particles have been proposed. For example, U.S. Pat. No. 5,330,778 (Stark; herein incorporated by reference in its entirety) describes a method for preparing microparticles using zein using pH alteration to form the zein microparticles. The method, however, produces zein particles with larger micron sizes and with a wide particle size distribution, which has significant drawbacks, for example, for in vivo use. A biomaterial used for human or animal applications needs to be safe and non-immunogenic. In general, upon in vivo administration (e.g., introduction into the body) of particles, phagocytic cells in the blood and tissues, which are responsible for immunological recognition and removal of foreign particles, can initiate an immune response depending on the physicochemical characteristics of the particles. The uptake by phagocytic cells is dependent upon both particle size and surface hydrophobicity of the foreign particle. Particles greater than about 500 nm in diameter are highly prone to phagocytosis. Additionally, particles with a hydrophobic surface are easily recognized by the phagocytic cells. For example, Lopez and Murdan reported that zein microspheres having a diameter of 1.36±0.036 μm are immunogenic and, consequently, are not suitable as a drug, vaccine or other therapeutic carrier (Lopez and Murdan, J Pharm Pharmacol 58 (2006) 769-774)
Accordingly, new methods are needed for preparing zein particles to render the particles useful for therapeutic and cosmetic applications. Also needed are new therapeutic carriers for the delivery of important therapeutic and cosmetic agents in a safe and effective manner, so as to overcome challenges associated with skin penetration, retention, stability, skin irritation, and follicular targeting.